This invention relates generally to the field of fiber optics and more particularly, but without limitation thereto, to a technique for rapidly joining fiber optic cable expected to undergo significant tensile loadings.
Land-locked fiber cable settings seldom encounter the need for a rapidly performed cable splicing wherein the splice is capable of significant tensile loadings. While some land-based cable is strung from overhead telephone poles and the like, posing possible tension on these lines, it is much more typical for the lines to run underground or elsewhere in supporting conduits. The sealing effect of such a splice needs only to resist common moisture or occasional flooding.
In the underwater environment, cable conditions can be much more trying. Besides having to deal with some-times extreme hydrostatic pressures, there are also tensile stresses that occur during the laying of these cables and their repair. In addition to the weight of the cable from ship to ocean floor, there are concerns of drag on the cable as it is payed-out from a dispensing ship.
Autonomous vehicles have made it possible to repair a great many fiber optic cables laid on the ocean floor. The vehicles are used to retrieve the faulty cable and bring it to the surface where a new span or length of cable can be spliced into place. In such repair scenarios time can be of the essence for some obvious and not so obvious reasons. Sea-state can wreak havoc with positioning a repair vessel. The rise and fall of the vessel can add and detract from the tension placed upon the cable. Further, prolonged suspension of the cable in the water column during repair is usually something to be minimized.
Because of sea condition, it is desirable to provide a cable splice that can be executed promptly, that ensures adequate sealing, and that withstands acceptable tensile stresses without self-destructing.
A great many designs for underwater cable splices exist as fiber optics are now extensively employed in the world""s waters. Typically these involve potting compounds that require time to cure. Many such splices incorporate numerous parts and complicated procedures, lengthening the time to complete the splice.
In U.S. Pat. No. 4,846,545, two examples of cable splice designs are illustrated. Shown in FIGS. 1 and 2 of this patent, respectively, are a bulky/rigid connector and a much more flexible connector. The bulky connector has many parts that must be precisely assembled. The flexible connector requires that mechanical strength members be swaged together. In either case, these methods add complexity to the splicing procedure and thereby lengthen the time for the splicing to be made.
For all such splices, their optical as well as mechanical attributes are considered important. These are characteristics that frequently are traded-off in the sense that mechanical strength is provided at the expense of optical quality or that optical losses are minimized at the expense of mechanics.
There is thus a need for a fiber optic cable splice that provides excellent optical and mechanical properties without unreasonably sacrificing one or the other. When such a splice is used in maritime environments, it is desirable that the splice be executed in a prompt and efficient manner.
The invention provides a technique for joining fiber optic cables that can be rapidly executed and that provides desirable optical and mechanical properties. An example of the invention can be used with a fiber optic cable containing a radially inner optical fiber, a buffer section radially surrounding the fiber, a strength member section radially surrounding the buffer section and an outer protective jacket radially surrounding the strength member.
This technique includes the steps of:
stripping each fiber optic cable to terminate in a length of bare optical fiber, followed by a length of the cable where the buffer section is made bare, followed by a length of the cable wherein the strength member is made bare;
fusion splicing the bare optical fibers;
disposing a hot-melt adhesive tube over the bare fused fibers, the bare buffer lengths, the bare strength member lengths and a portion of the outer protective jacket of each cable;
disposing an inner heat shrink tube over the hot-melt tube;
inserting an elongated strengthening rod between the hot-melt adhesive tube and the inner heat shrink tube, the rod extending longitudinally for substantially equal lengths beyond these tubes;
exposing the hot-melt adhesive tube, the rod and the inner heat shrink tube to heat wherein the hot-melt adhesive tube shrinks and seals around the fused fibers, bare buffer lengths, bare strength member lengths and the portions of the outer protective jacket of each cable and wherein said inner heat shrink tube shrinks to bind the rod to the hot-melt adhesive tube and its enclosed contents;
helically winding the cable around the lengths of the rod that extend beyond the hot-melt adhesive and heat shrink tubes;
disposing an outer heat shrink tube over the elongated strengthening rod; and
exposing the outer heat shrink tube to heat so as to bind the rod to the cable, the inner heat shrink tube and its enclosed contents.
Other objects, advantages and new features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanied drawings.